fix flaky integration test

# Bug report

Fixing https://github.com/canonical/pycloudlib/issues/369 should make the following test no longer flaky. I'm filing this issue as a reminder so that we re-add this test to CI once the bug is fixed in pycloudlib.

https://github.com/canonical/cloud-init/blob/cf72d7f37b2fb45d5d97113ec83d0f24e0fc818a/tests/integration_tests/modules/test_power_state_change.py#L55

Note to self: [this branch](https://github.com/holmanb/cloud-init/tree/holmanb/unflakify-power) contains the fix and makes test behavior slightly easier to undertand.